How to remove all of pytest output and keep only error messages from asserts in stderr

[Lorac]

We want to run pytest inside an environment where it's only helpful to get an exit code 0 without any output from pytest but given any failure, I would like to get the assert error messages from stderr.

We have not created a plugin yet, but we tinkered with cli options, as far as we can tell, we cannot use p no:terminal since it removes everything. We tried with --no-header, --no-summary, console_output_style=classic, etc. We have added > /dev/null` to our run to remove stdout. But when a test fails, we don't see the stderr output. We tried all the capture mode, not one of them worked.

Ideally, given pytest [some arguments] tests_to_run, it shouldn't output anything if passing, only exit code 0; otherwise, send the pytest.fail("message") or assert message to stderr.

Will I need a custom plugin?

[Lorac]

I was able to come up with this:

class X:
    def pytest_terminal_summary(self, terminalreporter, exitstatus, config):
        """Show failure messages only. Given it's used with -p no:terminal"""
        if exitstatus != 0:
            reports = terminalreporter.stats.get("failed", [])
            for report in reports:
                print(f"{report.longrepr}", file=sys.stderr)